Fluid treatment systems are known. For example, U.S. Pat. Nos. 4,482,809, 4,872,980 and 5,006,244 (assigned to the assignee of the present invention), the contents of each of which are hereby incorporated by reference, all describe gravity fed fluid treatment systems which employ ultraviolet (UV) radiation.
Such systems include an array of UV lamp frames which include several UV lamps each of which are mounted within sleeves extending between two support arms of the frames. The frames are immersed into the fluid to be treated which is then irradiated as required. The amount of radiation to which the fluid is exposed is determined by the proximity of the fluid to the lamps, the output wattage of the lamps and the fluid's flow rate past the lamps. One or more UV sensors may be employed to monitor the UV output of the lamps and the fluid level is typically controlled, to some extent, downstream of the treatment device by means of level gates or the like. Since, at higher flow .[.rams.]. .Iadd.rates.Iaddend., accurate fluid level control is difficult to achieve in gravity fed systems, fluctuations in fluid level are inevitable. Such fluctuations could lead to non-uniform irradiation in the treated fluid.
However, disadvantages exist with the above-described systems. Depending upon the quality of the fluid which is being treated, the sleeves surrounding the UV lamps periodically become fouled with foreign materials, inhibiting their ability to transmit UV radiation to the fluid. When fouled, at intervals which may be determined from historical operating data or by the measurements from the UV sensors, the sleeves must be manually cleaned to remove the fouling materials.
If the UV lamp frames are employed in an open, channel-like system, one or more of the frames may be removed while the system continues to operate, and the removed frames may be immersed in a bath of suitable acidic cleaning solution which is air-agitated to remove fouling materials. Of course, surplus or redundant sources of UV radiation must be provided (usually by including extra UV lamp frames) to ensure adequate irradiation of the fluid being treated while one or more of the frames has been removed for cleaning. Of course, this required surplus UV capacity adds to the expense of installing the treatment system.
Further, a cleaning vessel containing cleaning solution into which UV lamp frames may be placed must also be provided and maintained. Depending upon the number of frames to be cleaned at one time and the frequency at which they require cleaning, this can also significantly add to the expense of installing, maintaining and operating the treatment system.
If the frames are in a closed system, removal of the frames from the fluid for cleaning is usually impractical. In this case, the sleeves must be cleaned by suspending treatment of the fluid, shutting inlet and outlet valves to the treatment enclosure and filling the entire treatment enclosure with the acidic cleaning solution and air-agitating the fluid to remove the fouling materials. Cleaning such closed systems suffers from the disadvantages that the treatment system must be stopped while cleaning proceeds and that a large quantity of cleaning solution must be employed to fill the treatment enclosure. An additional problem exists in that handling large quantities of acidic cleaning fluid is hazardous and disposing of large quantities of used cleaning fluid is difficult and/or expensive. Of course open flow systems suffer from these two problems, albeit to a lesser degree.
Indeed, it is the belief of the present inventor that, once installed, one of the largest maintenance costs associated with prior art fluid treatment systems is often the cost of cleaning of the sleeves about the radiation sources.
Another disadvantage with the above-described prior art systems is the output of the UV lamps. Unfortunately, the UV lamps in the prior art systems were required to be about five feet in length to provide the necessary wattage of UV radiation. Accordingly, the UV lamps were relatively fragile and required support at each end of the lamp. This increased the capital cost of the system.
Further, due to the somewhat limited output wattage of the UV lamps in the prior art systems, a great number of lamps were often required. For example, certain prior art installations employ over 9,000 lamps. Such a high number of lamps adds to the above-mentioned costs in cleaning lamps as well as the cost of maintaining (replacing) the lamps.